Chromatography is a widely used analytical technique for the chemical analysis and separation of molecules. Chromatography involves the separation of one or more analyte species from other matrix component present in a sample. A stationary phase of a chromatography column is typically selected so that there is an interaction with the analyte. Such interactions can be ionic, hydrophilic, hydrophobic, or combinations thereof. For example, the stationary phase can be derivatized with ionic moieties that ideally will bind to ionic analytes and matrix components with varying levels of affinity. A mobile phase is percolated through the stationary phase and competes with the analyte and matrix components for binding to the ionic moieties. The mobile phase or eluent are terms used to describe a liquid solvent or buffer solution that is pumped into a chromatography column inlet. During this competition, the analyte and matrix components will elute off of the stationary phase as a function of time and then be subsequently detected at a detector. Examples of some typical detectors are a conductivity detector, a UV-VIS spectrophotometer, and a mass spectrometer. Over the years, chromatography has developed into a powerful analytical tool that is useful for creating a healthier, cleaner, and safer environment where complex sample mixtures can be separated and analyzed for various industries such as water quality, environmental monitoring, food analysis, pharmaceutical, and biotechnology.
Stationary phase synthesis methods may utilize grafting for attaching ion exchange sites to the surface of a substrate. Such materials have been used for many commercial ion exchange products. Other stationary phase synthesis methods may utilize a crosslinker for forming bulk ion exchange resins. One parameter used to adjust selectivity in bulk ion exchange resins is the mole percent of crosslinker. Applicant believes that there is a need to use a crosslinker in a grafting process to improve selectivity in grafted stationary phases. Under certain circumstances, the use of a covalent crosslinker is not possible during a normal graft processes due to the fact that a covalent crosslinker causes gelation of the graft solution. Applicant also believes that gel formation is irreversible and incompatible with a grafting process for manufacturing useful chromatographic stationary phases.
Applicant also believes that there is a need to provide stationary phases that can be cleaned of impurities should they become fouled. For example, a stationary phase designed for separation of small mono, di, and trivalent ions is often exposed to samples containing polymeric ions of the same net charge. Such polymeric ions tend to form a very strong complex with the stationary phase which can be extremely difficult to remove once the complex is formed. Stationary phases can be ultimately destroyed due to excessive exposure to polymeric or other highly charged species.